1. Field of the Invention
The present invention relates to systems and methods for providing postoperative pain relief and, more particularly, to such systems and methods for local, site-specific, time-released administration of an anaesthetic.
2. Description of Related Art
Anaesthetic medication is generally required postoperatively for alleviation of discomfort at the surgical site. It has been considered desirable to deliver such medication via a single puncture in order to avoid multiple injections adjacent an area that is already painful.
Two such systems are known to have been disclosed: Reese (U.S. Pat. No. Re. 35,192) teaches a cannula and catheter system that is fed by a spring-loaded syringe wherein the spring has nonlinear characteristics that effect a gradually decreasing delivery rate with spring expansion. LeFevre (U.S. Pat. No. 4,997,420) describes a portable drug delivery device for administering a medication at a constant and self-regulated rate. This device includes a spring-loaded syringe having a reverse-taper cylinder to compensate for the decreasing force exerted by the spring as it expands.
Medication-delivery pumps have been marketed for use in oncological applications to deliver chemotherapeutic agents and for the delivery of antibiotics (the "OutBound" pump, McKinley, Inc., Wheat Ridge, Colo., and others). This pump has a flow-control restrictor and a filter to remove particulates.
In some procedures such as orthopedic operations, a patient can feel very comfortable even immediately after surgery because an anaesthetic will have been delivered into the surgical site, such as a joint. Therefore, until that dose of anaesthetic wears off, the patient experiences less post-operative discomfort. When it does wear off, however, the patient is often dependent upon medication to relieve postoperative pain. Such medication may have side effects and may not alleviate the pain completely, as it is circulated systemically and takes time to reach the target site.